To date there are several types of rotational to linear converters in common use. Systems such as the conventional lead screw, drum and cable, and hydraulic or pneumatic cylinders are in common use in robotic and prosthetic devices. All the research into the design of artificial hands or grippers have used one of these methods, for example: MIT Hand, Salisbury Hand, and the Hitachi gripper. The complexity and consequently the cost of these drive mechanisms has not been lowered to match the sensory and computing power advances made in the field of robotics.
The object of the present invention is to provide an actuating mechanism which closely performs and maintains the same physical function and configuration as a muscle and tendon.
Another object is to show the ease of use of the present invention in a closed-loop system and to make obvious it lowers the cost of achieving controlled translational movement.
In the present invention the force is high when motion is small and the force increases as motion decreases. This is a valuable feature when being matched to hinged member designs where the force and motion are not the same for different positions in the moving member's swing. Methods are shown by which the invention's mechanical gain may be changed during actuating length. It is obvious if opposing ends of a rotating shaft are used then bidirectional actuation may be attained.
Briefly described, the twisted cord actuator includes a motor with an axial shaft to which, by a coupling, the single free end of two or more cords are attached. The opposing ends of the cords are attached to the moveable member. As the shaft rotates the cords are twisted around each other in helical fashion. Thus their combined length is shortened.
In this invention the rotating device represents the muscle and the twisting of the cords, the tendons. The twisting pair of cords may then be threaded through a sheath to act as a pull cable. For example, for use as a tendon for an artificial finger or robotic arm. The values of this invention are low cost, ease of use and variability of design. In most applications the present invention may be matched to the load by the careful selection of the motor, cord diameter, and cord length without the use of a gear reducer. This combination creates a low inertia resilient actuator.